Os 32SX

[Boos Boy]

Hi, I've just bought a magic 3D second hand with an os32SX in it. its the mark 1 as reviewed in RCME APRIL 2003. Yes its an old mag I have here.

 I'm a bit confused; it has a 10x4 prop on it, but the reveiwer Davie Mathews said he usually puts a 12.25x3.75 prop on these typ of planes; but put a 13x4 on it and it flew loads better, hovered at 1/2 throttle and enough to pull out of bad situations.

My question is whether the 13x4 is suitable and if he was using a tuned pipe? I'm running constest 10 fuel and standard OS32SX. I've got a 13x4 and 12.25x3.75 here; just don;t want to over heat the little engine but want the best performance I can get as trying to learn 3D.

Thanx.

[Tim Mackey]

For 3D style flying you need a large diameter prop.

This gives the thrust required for those silly (oops sorry meant extreme ) manoeuvres. This generally means a lower pitch in order to stay within a reasonable ratio of diameter to pitch ( unless you are wanting a "square" prop ratio.) The lower pitch will result in less top end speed ( which you dont really need anyway for 3D ) I cant say whether he was using a pipe or not, but the engine specs should give an indication of suitable maximum prop sizes and if you change the diameter up, then reduce the pitch down by the same amount and you should be in the ballpark. EG: recommended prop 10 X 7 ...then 9 X 8 would be OK as would 11 X 6 and so on.

SX 32 specs are

Practical rpm: 2,000-22,000
Output: 1.2 hp @ 18,000 rpm
Recommended Props: 10x6, 10.5x6, 11x6

I guess therefore that 12 or 13 x 4 or so should be fine...just watch that the revs dont drop off too much, indicating that the engine is labouring a little - this will lead to overheating, especially if fuel /oil ratio is a bit lean.

Of course there may well come a point when using such a big diameter may start to cause problems with torque rolling...but I guess the good 3D pilots would /could use this to improve things - rolling in the hover etc.

[Boos Boy]

Thanx for the reply. I'll take some props up thenteh field then later and give it a go; it pulls hard on the 10x4, so that gives me some idea; I'll just watch the revs as you said.

[Tim Mackey]

OK good luck, let us know how it was !

[Boos Boy]

Well, tried the standard 10x4, goes like a rocket.

11x4 was a bit better and loads of lift, take off in a few feet.

Tried a 12x6 but it didn't like that; didn;t have a 13x4 but trying it tomorrow as well as a 12.25x13x4. Also moved the CofG back to 5"; will go to 5.5" with 60g weight in the tail and weigh 4.1lbs like that.

Will let you know how I get on with the props tomorrow as long as the wind is reasonable; although these planes seems to fly anyway.